In the past, nitrile rubber (acrylonitrile-butadiene copolymer rubber) has been used as a material for hoses, tubes, and other automobile use rubber parts by taking advantage of its oil resistance, mechanical properties, chemical resistance, etc. Further, hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene copolymer rubber) which is obtained by hydrogenating the carbon-carbon double bonds in the polymer main chain of nitrile rubber is further excellent in heat resistance, so is used for belts, hoses, diaphragms, and other rubber parts.
In this situation, Patent Document 1 proposes a cross-linkable rubber composition which contains a hydrogenated nitrile rubber having α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units, a polyamine-based cross-linking agent, and a basic cross-linking accelerator. Using this composition, cross-linked rubber which is considerably improved in heat resistance and compression set resistance is obtained, but further improvement in compression set resistance has been sought.